The present invention relates to a method of determination and monitoring of a fuel mass stream which in the case of partial oxidation (gasification) of fine-grain up to pulverized fuel is supplied to a gasifier.
More particularly, the present invention relates to such a method which uses a radiometric density measurement of a fine-grain up to pulverized fuel conveyed with a gaseous medium, and a volume stream measurement, as well as uses process computers for conducting the required calculating operations.
During the partial oxidation of solid fuels, such as for example brown or stone coals or oil coke, it is necessary to guarantee that the fine-grain up to pulverized fuel, which in some cases can be brought to the desired grain size by a preceding grinding, be supplied to the gasifier with the gaseous or vaporous reaction media in a uniformly and quantitatively exactly defined stream. This is needed to provide in the gasifier constant operational conditions which guarantee a uniform quality of the produced partial oxidation gas. As gaseous or vaporous reaction, media, it is possible to use oxygen, air, or air enriched with oxygen, as well as an additional water vapor. When the fuel part in the reaction mixture in the gasifier is too low, this results because of the thus produced high ratio of oxygen to fuel, an undesirable increase in the operational temperature in the gasifier. If, to the contrary the fuel part in the reaction mixture in the gasifier is too high, this results in an incomplete reaction of the fuel with the oxidation medium. Thus there is a possibility that the not converted fuel particles deposit in the gasifier or together with the produced gas discharge from the gasifier. Moreover, under certain circumstances, this leads to breakdown of the reactor.
Therefore, it is necessary to determine and continuously monitor the fuel mass stream supplied to the gasifier. For solving this problem, there are methods which are described in the DE-OS No. 26 42 537 and DE-OS No. 27 57 032, in accordance with which the fine-grain up to pulverized fuel conveyed with the vaporous or gaseous reaction media is detected directly before the entrance of the gasifier by a radiometric density measurement, and the thus obtained value, with consideration of further value for the volume stream of the gaseous media and the density of the used fuel, is converted with the utilization of the process computer into a mass stream signal for the fuel supply. Thereby the safety locking of the gasifier can be controlled.
The utilization of the radiometric density measurement for the above mentioned purpose is already known. In accordance with this method, the radioactive ray penetrates in a predetermined measuring section the fuel conveyed with the gaseous reaction media and is weakened in dependence upon the penetrated weight per unit area (density.times.penetrated length). The residual ray is measured by a radiation detector and converted into a density-proportional direct-current signal. The measuring device includes a radioactive irradiator arranged at one side of the measuring section, and a detector located opposite to the irradiator at the other side of the measuring section. Between the radioactive irradiator and detector, a portion of a pipe through which solid fuel flows is located, the portion serving as the measuring section. The above described method provides for several advantages including contactless measurement, continuous measuring possibility, and relatively high reliability. Despite these advantages, the method described in both the above-mentioned DE-OS is not completely satisfactory because of the following reasons, and therefore can be improved. In the known method, the radiometric density measurement takes place in a pipe portion which in addition to the fuel and the fluidizing gas, also has the gaseous or vaporous reaction medium. This means, however, that the loading of the gas stream with fuel can in certain conditions lower to a limiting value in which an exact radiometric density measurement is no longer possible. Moreover, in accordance with the known method, the quantity of the fluidizing gas with which the fine-grain up to pulverized fuel leaves the fuel bin is left not considered. This quantity can, however, in certain conditions make a very high part of the gas quantity required for conveying the fuel, and therefore may not be neglected. Moreover, in accordance with the known methods, the introduction of the value for the specific weight of the fuel into the process computer is performed by hand, which leads to a further inaccuracy in counting the fuel mass stream.